Fibrous sheet material, composition therefor, and process of making



H Patented Nov. 29, 1932' GEORGE IE. DAVIS, 01 WALTHAM, MASSlLCHUSETTSFIBROUS SHEET MATERIAL, COMIOSITION THEREFOR, AND PROCESS OF MAKII IG NoDrawing.

The subject of this invention is fibrous sheet material, compositionstherefor, and a process of making the same. It is more particularlyconcerned with a sheet made of interfelted fibers on machinery of thepapermaking type and serviceable in producing shoe counters or otherarticleswhere a tough, waterproof sheet having good strength andtear-resisting qualities coupled with flexibil- Q ity or mellowness isdesired.

In the manufacture of commercial counterboard, it has been the practiceto use Waste fibrous material, such as old ropes, strings, bagging,etc., for not only is such material inexpensive, but it consists largelyof strong vegetable fibers, such as manila, hemp and jute, which impartto the resulting sheet the toughness essential for resisting thestresses 2 trouble with such raw-material is that, of

may to some extent be offset by cooking in al-- kaline liquors, such asa solution of sodium carbonate or a lime suspension, which serve ascleansing or purifying agents, and by blending strength-giving fibrousmaterial 'thereinto when the waste raw material is of an inferiornature. These expedients, however, fall short of being completelysatisfactory cures for the uncontrollable variability in the scrap orwaste fibrous material used.

Because of the low price at which counters must be sold, themanufacturer of counterboard is limited to the use of relativelyinexpensive raw materials. On'the other hand, he is obliged to selectraw materials and so process'them as to produce a counterboard havingthe desiderata hereinbefore enumerated. New rag stock is a desirable rawmaterial, but it, alone, is too expensive. Wood pulps, such as kraft andgroundwood, are in the desired low-price field, but a counterboard madetherefrom is likely to become hard, brittle and otherwise defectiveunder the stresses of use.

I have found that if a substantial proportion of sized orwaterproofedleather fibers in substantially unbeaten condition isincorporated into a beaten stock prepaied from celluto which countersare subjected in use. The

Application filed February 19, 1931. Serial No. 517,115.

lose fibers, and more especially wood pulp, and sized as usual, itbecomes possible to produce counterboards having enduring flexibilityor. mellowness and other qualities desired in counters. Such sized orWaterproofed 5 ly-tanned leather in water is not only accompa'nied bythe leaching out of considerable valuable Water-soluble constituent,including water-soluble tanning agent, from the leather, but further bythe generation of a distinctly acid condition in the beater water.

This acid condition in the beater Water precludes the application of theusual acid-precipitable sizing agents to the leather fibers. Thus,theaddition to the beaten leather stock of rosin size or of aqueousdispersions of sizing agents, such as waxes, asphalt, resins, andrubber, stabilized by soap or other acid-precipitab'le protectivecolloid, is attended by the precipitation of the sizing agentimmediately upon contact with the acid beater water, with the resultthat the sizing agent, rather than becoming attached to the leatherfibers, is liberated in the beater water and is lost along with thewater removed during formation into sheets on a paper machine.This'difliculty is overcome, as taught in that application, by finelyshredding the leather scrap into a fiuify mass of fibers capable ofbeing suspended in water to form a pulp which needs little, if any,beating for 'interfelting on a paper machine; The usual sizing agentscarried in an aqueous vehicle from which they are precipitable by acidsubstances are .then applied to the dry fibers as a fine spray or mistwhile the fibers are suspended in a gaseous medium, such as air. Thesizing agents are thus precipitated in situ on the acid fibers to formwaterproof envelopes or coatings which shield the fibers against loss ofappreciable water-soluble constituent when they are subsequentlysuspended in water to form a pulp. Such sized or waterproofed leatherfibers may be used in admixture with adopted in practice with eminentlysatisfactory results may be substantially as follows. A beater isfurnished with 100 parts by weight of kraft pulp and 100 parts ofmechanical wood pulp together with sufficient water to produce a stockconsistency of about 5%. The stock is beaten hard for about 8 to 12hours to develop the desired hydration or gelatinization of its fibers.To the beaten stock is then added about 5% of dry size, based on theweight of fiber, for instance rosin size or an aqueous dispersion ofparaffin wax stabilized by soap. If desired coloring ingredients mayalso be added. About 5% of alum or other acid substance is then added toprecipitate the sizing and coloring ingredients on the fibers.

The beater roll is then raised; about 100 parts of waterproofed leatherfibers prepared as hereinbefore described is then added to the sized,well-beaten, wood pulp; and the engine is operated with the roll raisedso as to efi'ect merely a homogeneous mixture of the sized fibercomponents. The sized leather fibers may be added in a thickenedcondition, e. g. in the form of a thick mass containing only about 40%water, or in the form of laps of about similar Water content produced ona wet machine, to avoid the addition of much water to the stock in theengine. The sized leather fibers may contain, say about 2% to 2Z0 sizingagent, based on the weight of dry The addition of sized leather fibersis made to the already beaten and sized wood pulp for the reason thatthe beating of such fibers is unnecessary and undesirable. Were suchfibers subjected to severe beating, much of their desirablewater-soluble content, including tanning agent, would be extractedtherefrom; and they would become markedly shortened in length.

The composite fiber furnish is withdrawn into a stuff chest, pumped tothe usual wet machine wherein it is diluted to a consistency of about1%, and run off'into sheets of the desired caliper or thickness, forinstance 3 to 3% irons, which is'the usual range of thickness ofcounterboard for both mens and womens shoes. (The iron, which is thestandard gage of measuring thickness of leather, equals 1/48 of aninch). The sheets are then dried, calendered, cut into counter blanks,and molded into counters by the usual method.

While my invention has been described as applied to the production ofcounterboard, wherein, so far as I am now aware, it has the greatestutility, the principles thereof may have application to the productionof sheet material useful for articles other than counters, or in theproduction of fiber products other than sheets. The novel fiber furnishwhich I employ may include Wood pulps, such as soda or sulphite pulp. Itmay include cellulose fibers differing in origin and in proportion fromthose given in the example, but it is preferable in the case ofcounterboard to use a preponderant proportion of cellulose fiberconsisting of a mixture of equal parts of kraft pulp and groundwoodpulp, as stated in the example. Not only are both these wood pulpsvirgin materials, but they are quite inexpensive, especially thegroundwood pulp. The kraft pulp is advantageous in that it lendsstrength to the product, especially after it is well beaten. While it ispossible to apply a waterproofing agent to the finely shredded leatherscrap without an aqueous vehicle, for instance in a liquid conditionbrought about by melting the size or by dissolving it in suitableorganic solvents of a readily volatile nature, it is, from thestandpoint of simplicity and low cost, distinctly preferable to workwith sizing or waterproofing agents carried by an aqueous vehicle andfrom which the agent is precipitated by mere contact with the acidleather fibers. If desired, the fixation of the sizing agent to theleather fibers so sized may then be ensured by the addition of asolution of an acid substance such as alum thereto.

What I claim is:

1. A composite fiber furnish comprising waterproofed, previously-tannedleather fiber in substantially unbeaten condition comingled withwell-beaten, sized cellulose fiber.

2. A composite fiber furnish comprising waterproofed, previously-tannedleather fiber in substantially unbeaten condition comingled withwell-beaten, sized wood pulp.

3. A composite fiber furnish comprising a subordinate proportion ofwaterproofed, previously-tanned leather fiber in substantially unbeatencondition comingled with a preponderant proportion of well-beaten, sizedwood pulp.

4. A composite fiber furnish comprising waterproofed, previously-tannedleather fibers in substantially unbeaten condition comingled withwell-beaten sized kraft pulp and mechanical wood pulp. said fibercomponents being present in substantially equal proportions.

5. An interfelted fiber sheet all of whose fibers are sized andcomprising previouslytanned leather fibers in substantially unbeatencondition and associated with substantial- 1y all of their water solubleconstituent, including tanning agent, and well-beaten cellulose fibers.

6. A process which comprises beating cellulose fiber in water until itis well-hydrated, sizing the resulting aqueous fiber suspension, andcomingling therewith sized,-previousl'ytanned leather fiber whilekeeping associated with such latter fiber substantially all ofitswater-soluble constituent, including tanning agent.

7 A process which comprises beating cellulose fiber in water until it iswell-hydrated, sizing the resulting aqueous fiber suspension, cominglingtherewith sized, previouslytanned leather fiber while keeping associatedwith such latter fiber substantially all of its water-solubleconstituent, including tanning agent, and interfelting the mixture ofsized fibers into sheets.

In testimony whereof I have aflixed my signature.

GEORGE F. DAVIS.

